None.
Roller cone bits, variously referred to as rock bits or drill bits, are used in earth drilling applications. Typically, these are used in petroleum or mining operations where the cost of drilling is significantly affected by the rate that the drill bits penetrate the various types of subterranean formations. There is a continual effort to optimize the design of drill bits to more rapidly drill specific formations so as to reduce these drilling costs.
One design element that significantly affects the drilling rate of the rock bit is the hydraulics. As they drill, the rock bits generate rock fragments known as drill cuttings. These rock fragments are carried uphole to the surface by a moving column of drilling fluid that travels to the interior of the drill bit through the center of an attached drill string, is ejected from the face of the drill bit through a series of jet nozzles, and is carried uphole through an annulus formed by the outside of the drill string and the borehole wall.
Bit hydraulics can be used to accomplish many different purposes on the hole bottom. Generally, a drill bit is configured with three cones at its bottom that are equidistantly spaced around the circumference of the bit. These cones are imbedded with inserts (otherwise known as teeth) that penetrate the formation as the drill bit rotates in the hole. Generally, between each pair of cones is a jet bore with an installed erosion resistant nozzle that directs the fluid from the face of the bit to the hole bottom to move the cuttings from the proximity of the bit and up the annulus to the surface. The placement and directionality of the nozzles as well as the nozzle sizing and nozzle extension significantly affect the ability of the fluid to remove cuttings from the bore hole.
The optimal placement, directionality and sizing of the nozzle can change depending on the bit size and formation type that is being drilled. For instance, in soft, sticky formations, drilling rates can be reduced as the formation begins to stick to the cones of the bit. As the inserts attempt to penetrate the formation, they are restrained by the formation stuck to the cones, reducing the amount of material removed by the insert and slowing the rate of penetration (ROP). In this instance, fluid directed toward the cones can help to clean the inserts and cones allowing them to penetrate to their maximum depth, maintaining the rate of penetration for the bit. Furthermore, as the inserts begin to wear down, the bit can drill longer since the cleaned inserts will continue to penetrate the formation even in their reduced state. Alternatively, in a harder, less sticky type of formation, cone cleaning is not a significant deterrent to the penetration rate. In fact, directing fluid toward the cone can reduce the bit life since the harder particles can erode the cone shell causing the loss of inserts. In this type of formation, removal of the cuttings from the proximity of the bit can be a more effective use of the hydraulic energy. This can be accomplished by directing two nozzles with small inclinations toward the center of the bit and blanking the third nozzle such that the fluid impinges on the hole bottom, sweeps across to the blanked side and moves up the hole wall away from the proximity of the bit. This technique is commonly referred to as a cross flow configuration and has shown significant penetration rate increases in the appropriate applications. In other applications, moving the nozzle exit point closer to the hole bottom can significantly affect drilling rates by increasing the impact pressures on the formation. The increased pressure at the impingement point of the jet stream and the hole bottom as well as the increased turbulent energy on the hole bottom can more effectively lift the cuttings so they can be removed from the proximity of the bit.
Unfortunately, modifications to bit hydraulics have generally been difficult to accomplish. Usually, bits are constructed using one to three legs that are machined from a forged component. This forged component, called a leg forging, has a predetermined internal fluid cavity (or internal plenum) that directs the drilling fluid from the center of the bit to the peripheral jet bores. A receptacle for an erosion resistant nozzle is machined into the leg forging, as well as a passageway that is in communication with the internal plenum of the bit. Typically, there is very little flexibility to move the nozzle receptacle location or to change the center line direction of the nozzle receptacle because of the geometrical constraints for the leg forging design. To change the hydraulics of the bit, it would be possible to modify the leg forging design to allow the nozzle receptacle to be machined in different locations depending on the desired flow pattern. However, due to the cost of making new forging dies and the expense of inventorying multiple forgings for a single size bit, it would not be cost effective to frequently change the forging to meet the changing needs of the hydraulic designer. In order to increase the ability of optimizing the hydraulics to specific applications, a more cost effective and positionally/vectorally flexible design methodology is needed to allow specific rock bit sizes and types to be optimize for local area applications.
The prior art has several examples of different attachable bodies used to improve the bit hydraulics. U.S. Pat. No. 5,669,459 (hereby incorporated by reference for all purposes) teaches the use of several different types of machined slots in the leg forging and a weldably attached body that mates to the machined slots and that directs the fluid from the interior plenum to the outside of the bit. One slot design allows the attachable body to be pivoted in one direction to radially adjust the exit vector of the nozzle. A second slot design uses a ball and socket type design that would allow the tube to be vectored both radially and laterally. However, in both of these designs it is difficult to align the vector angle, and both designs require costly fixtures to ensure the correct angle for the attached body. Furthermore, this type of slot is difficult and costly to machine. Moreover, the internal entrance to the weldable body is necessarily smaller than the machined opening of the slot to account for the variations in the nozzle body angles. This difference between the entrance to the attached tube and the machined slot opening creates a fluidic discontinuity in the path of the fluid from the center of the bit through the slot opening and into the tube. This discontinuity can cause turbulent eddy currents that can erode through the side wall of the bit causing premature bit failure. Such bit failures are unacceptable in drilling applications due to the high costs of drill bits and lost drilling time. A third slot design teaches a slot with only one orientation where the opening in the forging is closely matched to the entrance to the attachable body. This matched interface significantly reduces fluidic erosion increasing the reliability of the system. However, the slot does not include the ability to change the vector of the fluid system. This particular system directs the fluid parallel to the bit center line toward the hole bottom.
Consequently, it would be desirable to have a drill bit design that overcomes these and other problems.
An embodiment of the invention is a drill bit having an internal fluid plenum and that defines a longitudinal axis, a nozzle retention body having an upper end for keyed attachment to the drill bit body and a lower end for retention of a nozzle, the upper end including a fluid inlet that is in fluid communication with the internal fluid plenum and the lower end defining a fluid exit flow angle. The fluid exit flow angle is angularly disposed from the longitudinal axis, and may include a lateral component or a radial component. The lower end preferably includes a smaller cross-sectional area than the region above it due, for example, to chamfering. The outermost portion of the nozzle retention body may extend to any desired degree, including short of the full diameter of the drill bit or to the full diameter of the drill bit. The drill bit may include nozzle retention bodies defining exit flow angles that are the same as, or differ from, each other. The nozzle retention bodies may also hold a nozzle that ejects drilling fluid at the exit flow angle of the nozzle retention body or at some different angle.
Alternately, the invention may be understood to be a method to form a nozzle retention body suitable for engagement to a drill bit including the step of manufacturing an unfinished nozzle retention body including an upper end and a lower end, the upper end forming an inlet that transitions into a flowbore and the step of machining a nozzle receptacle passage through said lower end portion and toward the flowbore, the nozzle receptacle passage being at an angle with respect to the longitudinal axis passing through the center of the nozzle receptacle. The machining of the nozzle receptacle passage may include drilling a counterbore into the lower end portion. The flowbore may include a pivot point at which the nozzle receptacle passage meets the flowbore. The unfinished nozzle retention body may also be chamfered at its lower end. The method may also include the step of mounting the upper end of the nozzle retention body into keyed relationship with the body of the drill bit, and the step of welding the nozzle retention body to the body of the drill bit.